Definitions
The following definitions are employed throughout the following discussion:
carrier set—a set of one or more frequencies associated with a PSD mask of a particular xDSL Recommendation;
downstream—direction of transmission from the xTU-C to the xTU-R;
Galf—an octet having the value 8116; i.e., the ones complement of an HDLC flag;
initiating signal—signal which initiates a startup procedure;
initiating station—DTE, DCE and other associated terminal equipment which initiates a startup procedure;
message—framed information conveyed via modulated transmission;
metallic local loop—communication channel 5, the metallic wires that form the local loop to the customer premise;
responding signal—signal sent in response to an initiating signal;
responding station—station that responds to initiation of a communication transaction from the remote station;
session—active communications connection, measured from beginning to end, between computers or applications over a network;
signal—information conveyed via tone based transmission;
signaling family—group of carrier sets which are integral multiples of a given carrier spacing frequency;
splitter—combination of a high pass filter and a low pass filter designed to split a metallic local loop into two bands of operation;
transaction—sequence of messages, ending with either a positive acknowledgment [ACK(1)], a negative acknowledgment (NAK), or a time-out;
terminal—station; and
upstream: The direction of transmission from the xTU-R to the xTU-C.
Abbreviations
The following abbreviations are used throughout the following discussion:
ACK—Acknowledge Message;
ADSL—Asymmetric Digital Subscriber Line;
CDSL—Consumer Digital Subscriber Line;
DSL—Digital Subscriber Line;
FSK—Frequency Shift Keying;
HDSL—High bit rate Digital Subscriber Line;
HSTU-C—handshaking portion of the xDSL central terminal unit (xTU-C);
HSTU-R—handshaking portion of the xDSL remote terminal unit (xTU-R).
ITU-T—International Telecommunication Union—Telecommunication Standardization Sector;
NAK—Negative Acknowledge Message;
POTS—Plain Old Telephone Service
PSD—Power Spectral Density;
PSTN—Public Switched Telephone Network;
RADSL—Rate Adaptive DSL;
RTX—Request Retransmit;
VDSL—Very high speed Digital Subscriber Line;
xDSL—any of the various types of Digital Subscriber Lines (DSL);
xTU-C—central terminal unit of an xDSL; and
xTU-R—remote terminal unit of an xDSL.
1. Field of the Invention
The present invention is directed to a high speed communications device, such as, for example, but not limited to, a modem, a cable modem, an xDSL modem, a satellite communication system, a point-to-point wired, or a wireless communication system, that includes a handshaking or initializing protocol, and in particular, to an apparatus and method that provides error free communication by detecting errors and requesting the retransmission of errored communication messages.
2. Discussion of Background and Other Information
Recently, new communication methods are being proposed and/or developed to transmit data on a local twisted wire pair that uses a frequency spectrum above a traditional voice band (e.g., 4 kHz bandwidth). For example, various “flavors” (variations) of digital subscriber line (DSL) modems have been/are being developed, such as, but not limited to, for example, DSL, ADSL, VDSL, HDSL, SHDSL and SDSL (the collection of which is generally referred to as xDSL). Each particular xDSL technology requires a robust start-up or initialization technique.
The ITU-T has published several recommended procedures for initiating a data communication, the following subject matter of which is expressly incorporated herein by reference in their entireties:
1) Recommendation V.8, entitled “Procedures For Starting Sessions Of Data Transmission Over The General Switched Telephone Network”, published in September, 1994;
2) Recommendation V.8bis, entitled “Procedures For The Identification And Selection Of Common Modes Of Operation Between Data Circuit-Terminating Equipments (DCEs) And Between Data Terminal Equipments (DTEs) Over The General Switched Telephone Network”, published in August, 1996; and
3) Recommendation G.994.1, entitled “Handshake Procedures For Digital Subscriber Line (DSL) Transceivers”, published in June 1999. It is noted that this document is the final version of Temporary Document MA-006, that was published in March, 1999.
Documents (1) and (2), above, pertain to procedures for initiating a data communication over voice band channels. Document (3), above, pertains to initiating a data communication over xDSL channels.
Unfortunately, if a data reception error occurs in a message, even if the error is only a single bit in length, the data communication devices must completely restart, from the beginning, a handshake (initialization) procedure. Since initialization procedures often involve a plurality of messages or transactions, and thus, restarting a transmission from the beginning results in a significant loss of information and time. Thus, there is a need for an apparatus and method that minimizes an initialization recovery procedure, by retransmitting only the errored portion of a session instead of completely restarting the initialization procedure.